title: Radioimmunoassay of apolipoprotein a-ii.
abstract: A double antibody radioimmunoassay was developed for apolipoprotein A-II (apo A-II), one of the two major apoproteins of human high density lipoproteins (HDL). Apo A-II contains two identical polypeptide chains linked by a disulfide bond. A specific antiserum was raised in sheep. Tracer apo A-II was radiolabeled with 125I by the Bolton-Hunter technique. Reduction and carboxymethylation of apo A-II approximately doubled its immunoreactivity. Since normal sera were found to contain small amounts of monomeric apo A-II, this represented one potential source of error in the radioimmunoassay. Inclusion of 0.1 M sodium cholate in the assay system, however, led to identical immunoreactivity of dimeric apo A-II and the reduced and carboxymethylated protein. Radioimmunoassay using sheep anti-apo A-II detected 75% to 85% of the apo A-II contained in serum or HDL. Masked antigenic sites could be exposed by organic solvent extraction or, more simply, by dilution of serum samples in the buffer containing 0.1 M sodium cholate. Serum levels of apo A-II were measured in a population of consecutively and prospectively selected free-living subjects between 30 to 69 years of age. Levels were significantly (p less than 0.005) higher in females (n = 201; 42.0 +/- 10.3 mg/dl) than in males (n = 189; 39.0 +/- 8.4 mg/dl). Serum apo A-II levels correlated significantly with HDL-cholesterol levels but less strongly than apo A-I, the other major HDL apoprotein.
mesh_terms: D000328:Adult; D000368:Aged; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D016633:Apolipoprotein A-II; D001053:Apolipoproteins / Q000097:blood* / Q000276:immunology; D002021:Buffers; D003902:Detergents; D006801:Humans; D007106:Immune Sera / Q000032:analysis; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL / Q000302:isolation & purification; D008875:Middle Aged; D011863:Radioimmunoassay / Q000379:methods*; D012756:Sheep / Q000276:immunology
chemical_list: D000596:Amino Acids; D016633:Apolipoprotein A-II; D001053:Apolipoproteins; D002021:Buffers; D003902:Detergents; D007106:Immune Sera; D007457:Iodine Radioisotopes; D008075:Lipoproteins, HDL